U.S. patent application number 13/468648 was filed with the patent office on 2013-11-14 for method of manufacturing heterogeneous electrochemical capacitors having a double electric layer and of manufacturing and balancing the coulombic capacities of electrodes for use therein.
This patent application is currently assigned to UNIVERSAL SUPERCAPACITORS LLC. The applicant listed for this patent is Samvel Kazaryan, Gamir Kharisov, Sergey Litvinenko, Sergey Razumov. Invention is credited to Samvel Kazaryan, Gamir Kharisov, Sergey Litvinenko, Sergey Razumov.
Application Number | 20130298363 13/468648 |
Document ID | / |
Family ID | 49547506 |
Filed Date | 2013-11-14 |
United States Patent
Application |
20130298363 |
Kind Code |
A1 |
Kazaryan; Samvel ; et
al. |
November 14, 2013 |
METHOD OF MANUFACTURING HETEROGENEOUS ELECTROCHEMICAL CAPACITORS
HAVING A DOUBLE ELECTRIC LAYER AND OF MANUFACTURING AND BALANCING
THE COULOMBIC CAPACITIES OF ELECTRODES FOR USE THEREIN
Abstract
Manufacturing methods for the formation of positive electrodes
and the balancing of Coulombic capacities of positive and negative
electrodes for use in a heterogeneous electrochemical capacitor
(HES) having a PbO.sub.2|H.sub.2SO.sub.4|C system. Exemplary
methods make it possible to manufacture capacitors with both
non-formed and pre-formed positive electrodes. Capacitors produced
by the exemplary methods may be used, for example, as secondary
power sources to level loads of power networks, power electric
vehicles, cellular and mobile communications, emergency lighting
systems, telecommunications, and solar and wind energy storage
devices.
Inventors: |
Kazaryan; Samvel; (Troitsk,
RU) ; Kharisov; Gamir; (Troitsk, RU) ;
Litvinenko; Sergey; (Zelenograd, RU) ; Razumov;
Sergey; (Moscow, RU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kazaryan; Samvel
Kharisov; Gamir
Litvinenko; Sergey
Razumov; Sergey |
Troitsk
Troitsk
Zelenograd
Moscow |
|
RU
RU
RU
RU |
|
|
Assignee: |
UNIVERSAL SUPERCAPACITORS
LLC
Columbus
OH
|
Family ID: |
49547506 |
Appl. No.: |
13/468648 |
Filed: |
May 10, 2012 |
Current U.S.
Class: |
29/25.03 |
Current CPC
Class: |
H01G 11/86 20130101;
H01G 11/12 20130101; H01G 11/46 20130101; Y02E 60/13 20130101; H01G
11/04 20130101; Y02T 10/7022 20130101; Y02T 10/70 20130101; H01G
11/14 20130101 |
Class at
Publication: |
29/25.03 |
International
Class: |
H01G 9/155 20060101
H01G009/155 |
Claims
1. A method of manufacturing a heterogeneous electrochemical
capacitor with a double electric layer, the capacitor having at
least one polarizable negative electrode comprising activated
carbon materials, at least one non-polarizable positive electrode,
an electrolyte of sulfuric acid aqueous solution, and a porous
separator that electronically separates the positive and negative
electrodes, the method comprising: placing a pre-formed negative
polarizable electrode in a case; placing a non-formed positive
electrode in the case, the non-formed active material of the
positive electrode comprising lead and lead sulfate PbSO.sub.4);
causing the formation of the active material of the non-formed
positive electrode after the positive electrode is placed in the
case, by passing an electric current through the capacitor so as to
produce an electrochemical oxidation of the positive electrode
active material; and balancing the Coulombic capacities of the
positive and negative electrodes; wherein, after formation, the
active material of the positive electrode is comprised of lead
dioxide obtained only by electrochemical oxidation of lead and its
combinations, and lead sulfate.
2. The method according to claim 1, wherein the capacitor includes
at least one non-polarizable positive electrode plate and at least
one negative polarizable electrode plate, and wherein the porous
separator electronically separates the plates of the positive and
negative electrodes.
3. (canceled)
4. The method according to claim 1, wherein the active material of
the non-formed positive made is comprised of a mixture of lead,
lead oxide (PbO), red lead (Pb.sub.3O.sub.4) and lead sulfate
(PbSO.sub.4), which may occur in different combinations with
different mass ratios of the components.
5. The method according to claim 12, wherein the electric current
is passed through the capacitor after the case is evacuated.
6. (canceled)
7. The method according to claim 2, wherein the active material of
the negative electrode is a carbon material which is bonded to its
current collector with conductive glue.
8. The method according to claim 1, wherein the capacitor is filled
with the sulfuric acid electrolyte with a temperature in the range
of minus 35.degree. C.-plus 30.degree. C.
9. The method according to claim 8, wherein the density of the
electrolyte before its addition to the capacitor is not lower than
1.1 g/cm.sup.3.
10. The method according to claim 9, wherein after the electrolyte
is added to the capacitor, a preliminary wetting of the electrodes
and separator by the electrolyte is performed.
11. The method according to claim 10, wherein the duration of the
preliminary wetting is 10-30 minutes.
12. The method according to claim 10, wherein after a preliminary
wetting of the electrodes and separator by the electrolyte, the
case is evacuated in a vacuum chamber.
13. The method according to claim 12, wherein the duration of the
evacuation process is between 15-30 minutes.
14. The method according to claim 13, wherein the vacuum chamber
pressure is between 5-150 mm Hg.
15. The method according to claim 1, wherein the electric current
is a constant current or a constant current with different
profiles.
16. The method according to claim 15, wherein the duration of
formation of the positive electrode active material is determined
from the total mass of the active material and the formation
current.
17. The method according to claim 16, wherein the duration of the
positive electrode formation process is not more than 70 hours.
18. The method according to claim 1, wherein forced cooling of the
capacitor is employed during formation of the positive
electrode.
19. The method according to claim 1, wherein at the start of
formation of the positive electrode, the potentials thereof are
polarized toward the negative values during a time period of not
more than 40 minutes.
20. The method according to claim 17, wherein after formation of
the positive electrode, the capacitor is discharged to a voltage of
not lower than 0.7 V and then sealed.
21. A method of manufacturing a heterogeneous electrochemical
capacitor with a double electric layer, the capacitor having at
least one polarizable negative electrode comprising activated
carbon materials, at least one non-polarizable positive electrode,
an electrolyte of sulfuric acid aqueous solution, and a porous
separator that electronically separates the positive and negative
electrodes, the method comprising: placing a pre-formed negative
polarizable electrode in the case; placing a non-formed positive
electrode in the case, the non-formed active material of the
positive electrode comprising lead and lead sulfate PbSO.sub.4;
causing the formation of the active material of the non-formed
positive electrode after the positive electrode is placed in the
case, by passing an electric current through the capacitor so as to
produce an electrochemical oxidation of the active material
thereof; filling the case with the sulfuric acid aqueous solution
electrolyte; evacuating the case; and balancing the Coulombic
capacities of the positive and negative electrodes; wherein, after
formation, the active material of the positive electrode is
comprised of lead dioxide obtained only by electrochemical
oxidation of lead and its combinations, and lead sulfate.
22. The method according to claim 1, wherein the active material of
the non-formed positive electrode also contains lead oxide (PbO),
red lead (Pb.sub.3O.sub.4).
23. (canceled)
24. The method according to claim 21, wherein the case is filled
with electrolyte at a temperature of not higher than 35.degree.
C.
25. The method according to claim 24, wherein after filling of the
case with the electrolyte, a preliminary wetting of the electrodes
and separator by the electrolyte is performed.
26. The method according to claim 25, wherein the duration of the
preliminary wetting of the electrodes and separator is not less
than 5 minutes.
27. The method according to claim 25, wherein after the preliminary
wetting of the electrodes and separator by the electrolyte, the
case is evacuated in a vacuum chamber.
28. The method according to claim 27, wherein the duration of
evacuation is not less than 15 minutes.
29. The method according to claim 28, wherein the vacuum chamber
pressure is between 5-150 mm Hg.
30. (canceled)
31. The method according to claim 21, wherein the balancing of the
Coulombic capacities of the electrodes is performed by a constant
current or a constant current with different profiles.
32. The method according to claim 21, wherein the duration of
Coulombic balancing is determined by the aggregate Coulombic
capacity of the negative electrode and the balancing current.
33. The method according to claim 21, wherein forced cooling is
used during Coulombic balancing.
34. The method according to claim 27, wherein a continuous
evacuation of gases occurs during the Coulombic balancing
process.
35. The method according to claim 21, wherein after the Coulombic
balancing of the electrodes, the capacitor is discharged to a
voltage in the range of 0.8-0.7 V, and the capacitor is sealed.
36. The method according to claim 27, wherein the vacuum chamber
pressure is between 5-250 mm Hg.
37. The method according to claim 21, wherein the electrolyte has a
density that does not exceed 1.35 g/cm.sup.3 at a temperature of
25.degree. C. when the capacitor is maximally charged.
38. A method of manufacturing a heterogeneous electrochemical
capacitor with a double electric layer, the capacitor having a
plurality of polarizable negative electrodes comprising activated
carbon materials, a plurality of non-polarizable positive
electrodes, an electrolyte of sulfuric acid aqueous solution, and a
porous separator that electronically separates the positive and
negative electrodes, the method comprising: placing pre-formed
negative polarizable electrodes in the case; placing non-formed
positive electrodes in the case, the non-formed active material of
the positive electrodes comprising lead and lead sulfate
(PbSO.sub.4); causing the formation of the active material of the
non-formed positive electrodes after the positive electrodes are
placed in the case, by passing an electric current through the
capacitor so as to produce an electrochemical oxidation of the
active material of the positive electrodes; filling the case with
the sulfuric acid aqueous solution electrolyte; evacuating the
case; balancing the Coulombic capacities of the positive and
negative electrodes; and discharging the capacitor until the
voltage thereof reaches between about 0.7-0.8 volts; wherein, after
formation, the active material of the positive electrodes is
comprised of lead dioxide obtained only by electrochemical
oxidation of lead and its combinations, and lead sulfate.
39. The method according to claim 38, wherein after filling of the
case with the electrolyte, a preliminary wetting of the electrodes
and separator by the electrolyte is performed and the case is
subsequently evacuated in a vacuum chamber.
40. The method according to claim 39, wherein the duration of
evacuation is not less than 15 minutes and the pressure of gases in
the vacuum chamber is between about 5-150 mm Hg.
41. The method according to claim 38, wherein: balancing of the
Coulombic capacities of the electrodes is performed by a constant
current or a constant current with different profiles; the duration
of Coulombic balancing is determined by the aggregate Coulombic
capacity of the negative electrodes and the balancing current; and
a continuous evacuation of gases occurs during the Coulombic
balancing process.
Description
TECHNICAL FIELD
[0001] The present invention relates to double electric layer
("DEL") electrochemical capacitors. More particularly, the present
invention relates to a method of manufacturing DEL heterogeneous
electrochemical supercapacitors ("HES'") having balanced positive
and negative electrode Coulombic capacities.
BACKGROUND
[0002] Pre-formed, non-polarizable electrodes are commonly used to
manufacture different DEL HES', in particular, capacitors having a
PbO.sub.2|H.sub.2SO.sub.4|C system. In a HES having a
PbO.sub.2|H.sub.2SO.sub.4|C system, use is made of a positive
electrode with lead dioxide (PbO.sub.2) active material, such as is
shown, for example, in U.S. Pat. Nos. 6,195,252 and 6,842,331.
Electrodes with a lead dioxide active material are used as positive
electrodes for lead-acid batteries, and are currently manufactured
using various methods. A mixture of metal lead (Pb) powders and
different lead oxides (Pb.sub.3O.sub.4 and PbO) are frequently used
for the manufacture of positive electrodes with PbO.sub.2 active
material. A paste is manufactured by mixing powders and an aqueous
solution of sulfuric acid. The resulting paste is puttied in a
positive electrode grid and then dried. After the electrode is
dried it is formed. As a general rule, the amount of lead sulfate
(PbSO.sub.4) in the dry non-formed active material does not exceed
5%. The formation process makes it possible to oxidize all the
active material to a lead dioxide.
[0003] Positive electrodes are typically formed by one of two main
methods. According to a first method, positive electrode plates are
formed in combination with negative electrodes before the
associated lead acid battery or HES having a
PbO.sub.2|H.sub.2SO.sub.4|C system is formed. In order to
manufacture lead-acid batteries, both positive and negative
pre-formed electrodes are used. In the manufacture of a HES,
pre-formed positive electrodes are used.
[0004] According to a second method, positive and negative
electrodes are formed after assembly of a battery. The second
method is primarily used for the manufacture of advanced lead-acid
batteries, and is easier, ecologically safer, and less costly than
the first method.
[0005] When a formation method for a positive electrode is
available, it is possible to use positive electrodes pre-formed and
made of lead oxide. However, this method is not optimal, and does
not allow for the manufacturing of capacitors with high and stable
specific energy, capacity parameters, or improved cost. When a HES
with pre-formed positive electrodes is assembled, the positive
electrodes are fully charged, while the negative electrodes are
fully discharged. To provide for serviceability of a capacitor,
both the positive and negative electrodes need to be in a fully
charged state. Therefore, when a capacitor is manufactured using
formed positive electrodes, an additional process is performed
after assembly to balance the Coulombic capacities of the
capacitors' positive and negative electrodes.
[0006] The technology and process of balancing the Coulombic
capacities of capacitor electrodes' depends upon the design and
overall dimensions of the electrodes. In addition, known techniques
for balancing Coulombic capacities require labor-intensive, costly
and long procedures. Because high rates of oxygen recombination are
typical of all HES' having an aqueous electrolyte, the process of
balancing sealed capacitors becomes more complicated. In
particular, a HES having a PbO.sub.2|H.sub.2SO.sub.4|C system where
the porous carbon DEL electrode is negative, is quite complicated.
High oxygen recombination in the capacitor's negative electrode
results in high efficiency of the oxygen cycle and impedes the
evolution of oxygen from the capacitor during its charge, which in
turn appreciably decreases the efficiency of the balancing
process.
[0007] In one known method of forming and charging a DEL capacitor
negative polarizable carbon electrode, a HES is manufactured using
a pre-formed positive electrode with a PbO.sub.2/PbSO.sub.4 active
material and a negative electrode based on activated carbon
materials. An aqueous solution of sulfuric acid is used as an
electrolyte. The capacitor, prior to its sealing, is placed in a
sealed chamber through which an inert gas flow (nitrogen or argon)
is circulated. Thereafter, the capacitor is charged. The process of
charging the capacitor is complete when the potential of the
negative electrode reaches a pre-set value. After the potential
reaches this pre-set value, the capacitor is sealed. During the
charging phase, the positive electrode generates oxygen, and the
negative electrode produces hydrogen. To provide effective removal
of hydrogen and oxygen from the capacitor, separators and/or
electrodes having extended channels are used.
[0008] This method of forming and charging a DEL capacitor negative
polarizable carbon electrode has many drawbacks that prevent the
manufacture of capacitors with high specific energy parameters and
low cost. This method of capacitor manufacturing does not take into
account the current state of the art with respect to the
manufacture of PbO.sub.2/PbSO.sub.4 positive electrodes. This
omission makes it impossible to manufacture commercial capacitors
having wide applications. The aforementioned capacitor design
allows for only one plate of the positive electrode to be used;
making it impossible to manufacture a capacitor with high
capacitance and discharge energy. To manufacture capacitor systems
having high discharge energies by this known method, it is required
to connect many capacitor cells, which brings about an abrupt
deterioration of the specific parameters, an increase in cost and a
decrease in the reliability of capacitor system operation.
[0009] When capacitors having a PbO.sub.2|H.sub.2SO.sub.4|C system
are manufactured as described above, the pre-formed positive
electrode is fully charged. However, the negative electrodes are in
a discharged state. To provide a functional capacitor after
assembly, the Coulombic capacities of the positive and negative
electrodes need to be balanced. To make balancing the Coulombic
capacities possible, the negative electrode is overcharged. Because
the Coulombic capacity of the positive electrode is considerably
higher than that of the negative electrode, the process must be
repeated several times. This need to repeat the balancing step
increases the time and cost of the capacitor manufacturing
process.
[0010] Since the positive electrodes are in a charged state during
the initial stage of the Coulombic capacity balancing step, oxygen
is evolved in the positive electrode. The rate of the oxygen
evolution increases along with a growth of the positive electrode's
state of charge. The oxygen diffuses to the negative electrode and
discharges it, which prevents the balancing process. As a result of
this discharge, the negative electrode is not fully charged, and
the specific energy and capacity parameters of the capacitor do not
reach their maximum values. To effectively balance the Coulombic
capacities of the positive and negative electrode it is necessary
to charge the capacitor under conditions that ensure a full charge
of the negative electrode. For a maximum charge of the negative
electrodes of a HES, it is necessary to remove the oxygen from the
capacitor. The efficiency of the Coulombic capacity balancing
process depends upon the efficiency of the oxygen removal. The
oxygen removal process is particularly important for capacitors
having large electrodes.
[0011] According to the previously described known method, the
oxygen is removed during the Coulombic capacity balancing process
by a flow of inert gas. This method of oxygen removal has several
drawbacks. First, an inert gas flow may effectively remove the
oxygen only from the periphery of the electrodes. Since the oxygen
creates excessive pressure inside the capacitor case, the
penetration of the inert gas flow into the central portion of the
electrodes is impeded. Even high intensity inert gas flow will not
effectively remove oxygen from the central portion of the
capacitors. A non-uniform removal of oxygen from the capacitor will
result in a non-uniform charge of the negative electrodes.
[0012] Therefore, this method of oxygen removal does not provide
efficient balancing of electrode capacities across a broad range of
capacitor designs and sizes. It may only be effective for
capacitors having one positive plate and two negative plates of
small dimensions. Additionally, the use of an inert gas flow makes
it impossible to perform an effective and uniform removal of oxygen
during a Coulombic capacity balancing process. Thus, the use of
this known method will result in a strong and non-uniform heating
of the capacitor, which will have a negative affect on the
parameters of the non-polarized electrodes thereof.
[0013] Second, the inert gas may partially fill the pores of DEL
capacitor negative electrodes by displacing the electrolyte. As a
result, the polarization resistance of the polarizable electrodes
may increase while charging the electrodes. Additionally, the
potential of DEL capacitor negative electrodes may appreciably
shift toward lower values at low levels of charge. Consequently,
the manufacturing method described above does not allow for: 1) an
accurate and correct determination of the charge of the negative
electrode; 2) a full balancing of an electrode's capacities; or 3)
a high and maximum specific parameters of a HES.
[0014] In order to manufacture capacitors with high specific energy
and capacity parameters, activated carbon materials with large,
developed areas are frequently used. A large developed surface area
may be covered by pores having a diameter of about 0.5-3 nm.
Another portion of the surface is covered by pores of small
dimension making it difficult to fill with electrolyte. Therefore,
the value of the capacitance of activated carbon DEL capacitor
polarizable electrodes depends considerably on the rate of the
filling of the electrodes' pores by the electrolyte. An effective
filling of the polarizable electrodes' pores by the electrolyte is
important to provide for maximum energy and capacity parameters and
an appropriate balance of the Coulombic capacities. Depending on
the parameters of the porous structure and manufacturing process of
the DEL capacitor electrodes, the filling of small size pores by
the electrolyte may take several days under normal conditions. To
speed up this process, different methods of carbon electrode
wetting by the electrolyte are employed.
[0015] The values of the polarization resistance and potential of
DEL capacitor electrodes are related to the filling of the pores by
the electrolyte. A partial filling of the pores results in a DEL
capacitor electrode having elevated values of the polarization
resistance and the potential's polarization. Therefore, during the
charge of a HES there occurs a rather strong polarization of the
potentials toward the negative area of only the near surface layers
of the DEL capacitor negative electrodes, while the deeper layers
of the electrodes are charged to a lesser extent. (See, e.g., S. A.
Kazaryan et al., J. Electrochem. Soc., 153 (9), A1655-A1671,
2006).
[0016] In this case, immediately after the charge current of the
capacitors is turned off, the potential of the negative electrodes
shift unevenly toward positive values. Due to this effect, there
occurs decomposition of the electrolyte and evolution of hydrogen
in the capacitor's negative electrode in the area of the potentials
of the electrolyte's thermodynamic stability. (See, e.g., B. Pillay
and J. Newman, J. Electrochem. Soc., Vol. 143, No 6, 1996). A
similar effect takes place when oxygen is removed from capacitors
by an inert gas flow. A non-uniform effect of the inert gas on the
DEL capacitor electrodes results in uneven distribution of the
charge current density and the potential of the electrodes along
the surface area and thickness. In the portions of the DEL
capacitor electrodes where there is a strong effect of the inert
gas, the potential decreases and hydrogen is evolved. The hydrogen
displaces the electrolyte from the electrodes' pores. This, in
turn, brings about further growth of the polarization resistance of
the polarizable electrodes, which has a negative effect on the
parameters of the capacitors and the process of balancing the
Coulombic capacities.
SUMMARY
[0017] The present invention provides an effective method of
filling the pores of a DEL capacitor's carbon material electrodes
with electrolyte, including small size pores, and is also a more
effective method of balancing the Coulombic capacities of the
positive and negative electrodes in a HES. According to the present
invention, it becomes possible to manufacture a commercial HES with
both high specific energy parameters and low cost. Thus, the
proposed exemplary methods of manufacturing an HES make it possible
to manufacture capacitors that can be effectively used as a
secondary power source for leveling of electricity supply network
loads, floor electric vehicles, cellular and mobile communication
means, emergency lighting systems, telecommunication systems, and
solar and wind energy storage.
[0018] The present invention provides a solution for the commercial
manufacturing of a DEL HES having a PbO.sub.2|H.sub.2SO.sub.4|C
system by: using a non-preformed plate for the positive electrode,
by improving the method of balancing the electrodes' capacities,
and by a reduction in the duration of balancing when pre-formed
positive electrodes are used. When non-preformed positive
electrodes are used, the positive electrodes are formed as a
component of the capacitor after the assembly process. During the
formation of the capacitors' positive electrodes the Coulombic
capacities of the positive and negative electrodes are
simultaneously balanced. The methods of the present invention make
it possible to appreciably increase the specific energy parameters
of the capacitors, facilitate manufacturing, and decrease
manufacturing costs. Moreover, by utilizing a more effective method
of balancing the Coulombic capacities of a capacitors' positive and
negative electrodes when a pre-formed positive electrode is used,
the efficient commercial manufacture of the capacitors has become
possible.
[0019] Exemplary methods of manufacturing a DEL HES, the filling of
electrode pores with electrolyte, the formation of positive
electrodes, and the balancing of the Coulombic capacities of the
positive and negative electrodes according to the present invention
are explained by the following description of exemplary embodiments
and associated drawing figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1a is a cross-sectional end view of an exemplary HES
having positive and negative electrodes;
[0021] FIG. 1b is a cross-sectional front view of the HES of FIG.
1a;
[0022] FIG. 2a is a cross-sectional end view of an exemplary DEL
negative electrode of the present invention;
[0023] FIG. 2b is a front view of the negative electrode of FIG.
2a;
[0024] FIG. 3a is a cross-sectional end view illustrating the
bonding of carbon plates to the current collectors of exemplary DEL
electrodes according to the present invention;
[0025] FIG. 3b is a front view of FIG. 3a;
[0026] FIG. 4 illustrates a rolling process for joining carbon
plates to a DEL electrode;
[0027] FIG. 5 is a diagram of an installation designed to fill a
HES with electrolyte;
[0028] FIG. 6 is a diagram of an installation designed to balance
the Coulombic capacities of the positive and negative electrodes of
a HES;
[0029] FIG. 7 is an illustration of time dependences of voltages of
HES #1, #3 and #4 as described below, during formation of their
positive electrodes;
[0030] FIG. 8 is an illustration of time dependences of temperature
of HES #1, #2 and #3 as described below, during formation of their
positive electrodes;
[0031] FIG. 9 is an illustration of time dependences of voltages of
HES #1 and #2 as described below, during charge and discharge by 15
A constant current with 140 Ah Coulombic charge capacity at
25.degree. C. temperature;
[0032] FIG. 10 is an illustration of time dependence of voltage (U)
and temperature (T) of HES #5 as described below, during formation
of its positive electrodes;
[0033] FIG. 11 is an illustration of time dependence of voltage of
HES #5 as described below, during charge and discharge by 25 A
constant current with the Coulombic charge capacity of 125 Ah (1),
175 Ah (2) and 250 Ah (3) at 25.degree. C. temperature;
[0034] FIG. 12 is an illustration of time dependence of voltage (U)
and temperature (T) of HES #6 as described below, during the
balancing of the Coulombic capacities of the positive and negative
electrodes; and
[0035] FIG. 13 is an illustration of time dependence of voltage of
HES #6 during charge and discharge by 13 A constant current with
the Coulombic charge capacity of 75 Ah (1), 100 Ah (2) and 110 Ah
(3) at 25.degree. C. temperature.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT(S)
[0036] The specific energy, capacity parameters, cycle life,
stability of operation, and cost of a HES are closely related to
its electrochemical and physical properties, its design, the
properties of the selected electrolyte, the associated method of
manufacturing employed, and the cost of the capacitors' components.
The unique parameters and properties of activated carbon materials
makes it possible to manufacture electrodes for a DEL HES. HES'
having different systems have been developed and manufactured.
These capacitors have specific energy and power parameters of
practical importance and a high cycle life. Of all known HES',
those having a PbO.sub.2|H.sub.2SO.sub.4|C system have the highest
specific energy parameters and lowest cost.
[0037] The active material of a positive, non-polarizable electrode
in a HES having a PbO.sub.2|H.sub.2SO.sub.4|C system is a mixed
phase of lead dioxide and lead sulfate. A DEL negative electrode is
made of a material based on conductive activated carbon attached to
a current collector. During charging of a HES having a positive
electrode with an active material of lead sulfate, the lead sulfate
is partially oxidized to lead dioxide. In the negative electrode,
an electric charge and energy are accumulated in the DEL. When the
capacitor is discharged, an inverse processes take place in its
electrodes. Despite the fact that different electrolytes may be
used, the highest parameters are obtained when sulfuric acid is
used, as described in U.S. Pat. No. 6,195,252.
[0038] When such a positive electrode is fully charged, its active
material contains only lead dioxide. The equilibrium potential of
this electrode at room temperature and about a 1.26 g/cm.sup.3
electrolyte density is approximately 1.7 V (in relation to SHE
potential). During the discharge of a HES, the lead dioxide in the
positive electrode transitions into lead sulfate (PbSO.sub.4),
producing a mixed phase of PbO.sub.2 and PbSO.sub.4 in the active
material of the positive electrode of a partially discharged HES.
The ratio of PbO.sub.2 and PbSO.sub.4 in the active material of the
positive electrode depends on the capacitor's design and voltage.
Usually, at a 100% depth of positive electrode discharge, the
coefficient of utilization of active materials is about 55-70%,
subject to the porous spatial structure of the active material
(i.e. when the positive electrodes are fully discharged only 55-70%
of the lead dioxide transitions to lead sulfate). Since lead
dioxide has high conductivity, and lead sulfate is a dielectric,
the serviceability of the electrode's active material is related to
the content of lead dioxide in the active material. When the
content of lead dioxide in the active material is below about 30%,
the resistance of the active material grows dramatically and the
positive electrode loses its serviceability. Therefore, the maximum
Coulombic capacity of the negative electrodes should not be higher
than the Coulombic capacity of the positive electrodes in the
maximum range of a HES operating voltage.
[0039] The cycle life of a HES is essentially determined by the
cycle life of its non-polarizable electrode. The cycle life of a
non-polarizable positive electrode having PbO.sub.2/PbSO.sub.4
active material depends on the depth of discharge, state of charge,
operation temperature, and values of charge-discharge currents. As
the depth of charge, state of charge, and operation temperature of
the positive electrode increase, the rate of decrease of the
electrode's Coulombic capacity grows along with the increase of the
number of the charge-dicharge cycles. This results in a decrease of
the cycle life of the positive electrode.
[0040] To provide a HES with a high cycle life, DEL electrodes
having a Coulombic capacity several times lower than the Coulombic
capacity of the non-polarizable electrode are selected, as is
described in, for example, U.S. Pat. No. 6,222,723. In the present
invention, Coulombic capacity of a HES is determined by the
Coulombic capacity of the DEL electrode. A decrease in the
Coulombic capacity of the non-polarizabe electrode will not cause a
decrease in HES Coulombic capacity or in HES energy parameters. The
cycle-life of a HES increases along with an increase in the ratio
of the capacities of its non-polarizable and polarizable
electrodes.
[0041] While at high levels of charge and discharge, a decrease in
the capacity of a positive electrode having a PbO.sub.2/PbSO.sub.4
active material is mostly determined by a change in the porous
structure and phase composition of its active material. A decrease
in the capacity at heavy overcharge is related to a change in the
electrophysical properties and structure of the transition layer of
the current collector's surface-active material interface. As
positive electrode overcharge increases, the capacities decrease at
a faster rate with an increase in the depth of the charge-discharge
cycle.
[0042] For the manufacture of a sealed HES, where containment is
provided by the oxygen cycle, it is necessary to select an optimal
ratio of Coulombic capacities in the positive and negative
electrodes and the state of charge of the positive electrodes.
Since the rate of the hydrogen oxidation in the positive electrode
of a HES having a PbO.sub.2|H.sub.2SO.sub.4|C system is negligible,
the design of a HES should ensure that any evolution of hydrogen is
ruled out in the negative electrode during HES operation, including
cases of significant overcharging. This ensures reliable and safe
operation of the HES.
[0043] The specific energy and capacity parameters of sealed
capacitors are related to the parameters and efficiency of the
oxygen cycle. During the capacitor's charge, the oxygen evolves in
the positive electrode and diffuses to the negative electrode,
where the oxygen is reduced to water with heat generation. In
parallel with the reduction of oxygen, the capacitor's negative
electrode gets discharged. The process of oxygen evolution in the
positive electrode depends on such parameters as the electrode's
state of charge, whether the electrode and electrolyte are of a
material having low overpotential of oxygen evolution, the phase
composition of lead dioxide, the value of the charge current, and
the electrolyte temperature. During the charge of a positive
electrode having a PbO.sub.2/PbSO.sub.4 active material, the
evolution of oxygen becomes noticeable only after 80-85% of the
state of charge--subject to the particular method of electrode
manufacture and the value of the charge current. When positive
electrodes are charged in the 80-100% range of their charge
capacity, the rate of oxygen evolution increase along with
increases to the state of charge and the value of the charge
current.
[0044] An increase in the rate of oxygen evolution is accompanied
by an increase in the rate of the oxygen cycle and an increase of
the capacitor's temperature. The charge of a capacitor having a
high oxygen cycle rate brings about two main negative consequences.
First, recombination of oxygen takes place not only on the surface,
but also penetrates deep into the DEL negative electrode. A
long-time recombination of oxygen during capacitor charging brings
about a considerable increase in the water amount and a decrease in
electrolyte concentration in pores of the negative electrode. This
results in an increase in capacitor polarization resistance, which
brings about additional overheating. Second, the evolution of
oxygen at the initial stage of the charging process reduces the
energy and Coulombic efficiency of the capacitor, makes achieving a
maximum charge impossible, and also makes it impossible to produce
a capacitor with high specific energy parameters. Extended
operation of a capacitor having an increased oxygen cycle is
accompanied by a considerable overcharge of its positive
electrodes, which brings about a decrease in the cycle life of the
positive electrodes, and of the capacitor as a whole.
[0045] Therefore, in order to manufacture a sealed
PbO.sub.2|H.sub.2SO.sub.4|C HES with high specific energy and
capacity parameters, high Coulombic and energy efficiency, high
cycle life, and stable parameters during extended operation, it is
important to properly select the parameters of the negative
electrodes and a method of optimally filling the pores thereof with
the electrolyte.
[0046] DEL negative electrodes in a HES are usually made of
different activated carbon materials. The potential zero charge
(pzc) of most activated carbon materials in aqueous sulfuric acid
solution is between about 0.2-0.3 V (in relation to SHE), subject
to crystallographic and physical properties. Activated carbon
materials have high chemical stability in different electrolytes,
including aqueous sulfuric acid solution. It is only at a potential
higher than about 1.0-1.1. V (in relation to SHE) that oxidation of
the activated carbon materials takes place.
[0047] When there is a shift toward the negative area of
potentials, the potential of the carbon materials is well
polarized. The high overpotential of hydrogen evolution makes it
possible to polarize carbon materials with low current densities to
a potential value of about minus 0.45-0.5 V (in relation to SHE
potential) without any evolution of hydrogen. A subsequent decrease
in the potential of the carbon material DEL electrodes is
accompanied by an increase in the rate of hydrogen evolution.
[0048] During polarization toward the area of negative potential,
both the Ohmic resistance and polarization resistance of the carbon
DEL electrodes increase. The increase in the resistance brings
about an Ohmic shift in the potential value toward negative values.
The value of the potential Ohmic shift depends on the density of
the charge current, structure, and state of electrode charge. At
high densities of charge current and a high state of charge of the
negative electrodes with high values of Ohmic and polarization
resistance, the potential of the electrodes shifts to a value of
about minus 1.2 V. There is no noticeable evolution of hydrogen,
and as soon as the charge current is turned off, the potential
increases quickly to a value of about minus 0.5-0.55 V.
Accordingly, any belief that the evolution of hydrogen in carbon
electrodes becomes noticeable only at a potential of minus 1.2 V is
erroneous.
[0049] It follows from the above that after the manufacture of a
HES having a PbO.sub.2|H.sub.2SO.sub.4|C system with formed
positive electrodes, the EMF is about 1.4-1.5 V, subject to the
properties of the negative electrodes. The maximum allowable
voltage of a HES during discharge by low currents is about 0.7 V
and the equilibrium value of EMF in the maximum charged state of a
HES is about 2.15-2.2 V. In order to increase the reliability of
HES operation, it is desirable to increase the minimal discharge
voltage of the capacitor to a value of about 0.8 V.
[0050] The capacitance of carbon material DEL electrode depends on
the potential of the electrode. As an electrode's potential
decreases, the capacitance of the electrode increases. Therefore,
an increase in HES voltage results in a considerable increase of
the capacitances and specific energy parameters.
[0051] During the charge and discharge of DEL electrochemical
capacitors, the electric charge and potential energy of the
polarizable electrode DEL are unevenly distributed by volume (i.e.,
during the charge and discharge of the capacitor, a volume
polarization of the electric charge takes place, and accordingly,
the potential energy of the polarizable electrode DEL takes place).
As soon as the charge and discharge currents are turned off,
redistribution of the DEL electric charge and a change of the
electrode potential take place in the volume of the polarizable
electrode (i.e., self-depolarization of the potential and energy of
the DEL electrode takes place). (See, e.g., S. A. Kazaryan et al.,
J. Electrochem. Soc., 153 (9), A1655-A1671, 2006). This process is
accompanied by a leveling of the polarizable electrode potential by
volume, and by the loss of a portion of the capacitor's stored
energy. During the self-depolarization of energy, after the charge,
there is an accelerated decrease in capacitor voltage. Conversely,
when the discharge current is turned off, capacitor voltage
increases slowly. The lost energy is evolved as Joule heat and is
determined by the flow of convection currents in the polarizable
electrode.
[0052] The value of the energy of polarization is related to the
parameters and design of the polarizable electrode, the design of
the capacitor, and the modes of its charge and discharge.
Polarization of energy in a HES with high energy density has a
practical significance and a considerable effect on the energy,
capacity, and operation parameters of a HES. The value of
self-depolarization of the DEL electrode potential also depends on
the filling of the electrode pores with electrolyte and the rate of
balance of the Coulombic capacities of the positive and negative
electrodes. Inefficient filling of the pores of DEL electrodes with
electrolyte results in charge and discharge of only the electrodes'
near-surface areas. As a result of inefficient electrolyte filling,
a strong self-polarization of DEL electrode potential occurs,
bringing about a substantial loss of stored energy and a decrease
in the energy efficiencies of the charge-discharge cycles of the
HES.
[0053] As illustrated by the following exemplary embodiments of the
present invention, it is possible to appreciably minimize losses of
energy by determining the effect of DEL electrode potential
depolarization after the charge and discharge of capacitors with
high currents. Apart from an increase in the specific energy
parameters, exemplary capacitor manufacturing methods of the
present invention bring about a considerable increase in the energy
efficiency and stability of the energy parameters of a capacitor's
charge-discharge cycle. The efficiency with which electrolyte can
be made to fill the pore volume of an active carbon DEL electrode
depends on the dimensions of the pores, the wettability of the
electrode, and the spatial structure of the electrode.
[0054] The wettability of carbon electrodes by an electrolyte
depends at least in part on the density of the states of electronic
levels on the surface of the pore walls. During carbon electrode
potential polarization toward negative values, an increase in the
density of the surface states takes place, and the wettability of
the electrode increases. Prior to the present invention, the pore
volume of DEL electrodes was filled with gas before assembly of the
associated capacitor, which impedes the effective and fast filling
of the pores by the electrolyte. An effective and fast filling of a
carbon electrodes' pores by an electrolyte may be accomplished by
simultaneous removal of gases from the pores and a strong
polarization of the electrodes' potential toward the area of the
negative values.
[0055] FIG. 1a illustrates an exemplary DEL HES 1 having a
PbO.sub.2|H.sub.2SO.sub.4|C system and comprising a number of
positive electrodes 2 of an active PbO.sub.2/PbSO.sub.4 material, a
number of porous carbon plate negative electrodes 3, with
associated negative electrode current collectors 4, and a porous
separator 5. The electrodes and separator are wetted by a rated
amount of electrolyte. The electrode pack is placed in a case 6
with a seal 7 surrounding the electrodes' terminals 8 (shown in
FIG. 1b).
[0056] FIG. 1b illustrates the HES' connection clamps 9 and shows
that the HES is equipped with an emergency valve 10. The present
invention provides exemplary methods of manufacturing HES'.
[0057] One exemplary embodiment of the method of the present
invention is the manufacturing of a capacitor 1 having non-formed
positive electrodes 2. The formation of positive electrodes 2 and
balancing of the Coulombic capacities of the positive and negative
electrodes 2 and 3 is performed after the assembly of the
capacitor. This embodiment allows the manufacturing of capacitors
with high specific energy parameters at a low cost and without a
complicated manufacturing process. Another exemplary method of the
present invention is the manufacturing of the capacitor 1 using a
preformed positive electrode 2. In this embodiment, the Coulombic
capacities are balanced after the assembly of the capacitor.
[0058] Through research it was established that the life cycle of a
sealed HES having a PbO.sub.2|H.sub.2SO.sub.4|C system is related
to the depth of discharge and the state of charge of the positive
electrodes. As the depth of discharge and state of charge of the
positive electrodes increase, the cycle life of the capacitor
decrease. An increase of the depth of discharge of the positive
electrodes results in an increase of the specific energy parameters
of the capacitors. The research established that the cycle life of
the positive electrode in the sealed capacitor increases
considerably when the state of charge of the positive electrode
does not exceed 90-95% of the maximum Coulombic capacity. The cycle
life of the positive electrodes decreases considerably when the
depth of discharge is more than 85% of the maximum Coulombic
capacity (i.e., the positive electrodes of the HES have a high
cycle life when the state of the charge does not exceed about
90-95% and the depth of discharge is about 75-80% and as the depth
of discharge decreases the cycle life of the positive electrodes
and capacitor increase). In HES-capacitors with high life cycle
life, the Coulombic capacities operation ratio may reach 75% of
their maximum capacities.
[0059] During the balancing of the Coulombic capacities of the
positive and negative electrodes 2 and 3, the states of charge of
the capacitor's electrodes reach maximum values. Therefore, the
method of manufacturing capacitors should be capable of providing
90-95% of the state of charge of the positive electrode 2 at 100%
state of charge of the negative electrode 3 when the capacitor has
the optimal state of charge. Exemplary methods of the present
invention provide for this by providing optimal balancing of the
electrodes' Coulombic capacities, unique properties of the DEL,
active carbon, negative electrode, and other design features
described below.
[0060] When the positive electrodes 2 are formed after the assembly
of the capacitors 1 or after balancing of the Coulombic capacities
of the electrodes in capacitors with pre-formed positive electrodes
in the absence of oxygen, the positive and negative electrodes 2
and 3 are charged to the maximum degree. When the capacitors 1 are
discharged to the voltage of 0.8 V, immediately after the formation
of the positive electrodes 2 or balancing of the Coulombic
capacities of the positive and negative electrodes 2 and 3, the
depth of discharge of the positive electrodes 2 may reach the
maximum value of the Coulombic capacities of the negative
electrodes 3. The sealing of the capacitor 1 immediately after the
discharge to a voltage of about 0.7-0.8 V by way of an installed
emergency valve 10 results in the state of charge of the negative
electrode 3 in subsequent charges of the capacitor never 100% due
to the oxygen cycle; irrespective of the duration and method of the
charge process. Consequently, the positive electrode 2 of the
capacitor 1 after being sealed is also not charged to the maximum
value. Research showed that when the maximum Coulombic capacity of
the negative electrodes 3 is less than 30% against the maximum
Coulombic capacity of the positive electrodes 2 after sealing the
HES, the Coulombic capacity of the negative electrodes 3 decreases
by about 5-10% (i.e., at the maximum state of charge of the
capacitors, the state of charge of the positive electrodes 2 does
not exceed 90-95% providing protection against overcharge of the
capacitors' positive electrodes 2 and the high cycle life).
[0061] Currently in the manufacturing of electrochemical capacitors
having DEL polarizable electrodes based on carbon materials, the
carbon materials and current collectors of the electrodes are
connected by mechanical clamping of the current collectors and
carbon materials. This method of electrode manufacturing often
requires excessively high external mechanical pressure on the
capacitors' case 6 to provide for stable resistance and energy and
power parameters. The current process makes the manufacturing
process more complicated, decreases the specific energy parameters,
and increases the cost. However, as shown in FIGS. 2a-2b and 3a-3b,
a negative electrode 11 is manufactured by pasting the carbon
plates 3 to the current collectors 4. The surface of the current
collectors 4 have a conductive protective coating 12 and a thin
conductive adhesive layer 13 applied (this layer is based on high
conductive carbon materials and polymers which have high adhesion
with carbon plates and current collectors and resistance to aqueous
solution of sulfuric acid). The pasting of the carbon plates 3 and
current collectors 4 provide for a low and stable "carbon
plate-current collector" contact resistance making it possible to
manufacture a whole negative electrode 11 and 14. This exemplary
method facilitates the manufacturing of a HES and lowers the
associated costs. The use of whole negative electrodes in a HES
makes it possible to operate the capacitor without any external
mechanical pressure on its case 6.
[0062] The carbon plates 3 and current collectors 4, having a
protective coating, may be pasted using other methods. FIG. 4 shows
one exemplary method of pasting 15 wherein the joint carbon plates
3 and current collector 4 with a protective coating 12 and adhesive
layer 13 are rolled using cylinder rolls 16 that revolve
synchronously. The gap between the cylinder rolls 16 is fixed to a
desired thickness of the carbon plates 3, current collectors 4, and
mechanical pressure on the electrode. Research has shown that the
pasting method 15 provides for a low and even "current
collector-carbon plate" 11 and 14 contact resistance at about
0.5-0.7 kg/cm.sup.2 pressure of the rolls on the electrode. The
even pattern of the contact resistance of the current collectors 4
and carbon materials along the entire surface of the negative
electrodes 3 is one of the most important conditions in obtaining a
HES with high specific energy parameters. The even pattern of the
contact resistance provides for an even charge and discharge along
the height of the electrodes, in particular in larger
electrodes.
[0063] In an exemplary method of manufacturing a capacitor 1, an
electrode pack is assembled with the desired count of the positive
2 and negative 11 electrodes and placed in the case 6. FIG. 2b
illustrates an exemplary embodiment where there is a positive
electrode 3 having only one plate wherein use is made of the
negative electrodes 14. In the manufacturing of the capacitor 1
with a high number of plates of positive and negative electrodes 2
and 11, the end plates of the negative electrodes are made of the
electrodes 14. This design is preferable because it provides for an
identical depth of operation of all the plates of the negative
electrode. Terminals 8 are cast from a lead alloy with the jumpers
of the connection lugs of the positive and negative electrodes'
current collectors. The capacitor's case is fixed and the cover is
welded to the case and the capacitor's terminals 7 are sealed.
[0064] The filling of the capacitor 1, having non-formed positive
electrodes, with electrolytes is performed after the assembly of
the capacitor. The electrolyte is filled into the capacitor through
an opening designed for the emergency valve 10. The amount and
concentration of the electrolyte in the capacitor depends on the
design, value of the capacitance, and purpose of each particular
capacitor. The correct choice of amount and concentration of the
electrolyte is substantially related to specific energy parameters,
cycle life, and stability of the parameters of a HES and has
considerable effect on the listed parameters. To provide a reliable
sealing of the capacitor it is necessary to provide effective
diffusion of oxygen in the electrodes and separator. The efficiency
of the oxygen diffusion to the negative electrodes will increase
with an increase of the quantity of the electrodes' and separator's
pores that have no electrolyte i.e. the pores of the capacitor's
electrodes and separator shall be partially filled with the
electrolyte (i.e., when a HES is charged, both the volume and the
concentration of the electrolyte increase and decrease during the
discharge). Since a change in concentration and volume of the
electrolyte takes place during the charge and discharge of a HES
having a PbO.sub.2|H.sub.2SO.sub.4|C system, the rate of the
filling of the pores of the electrodes and separator changes during
charge and discharge. Research of HES with different designs and
different values of capacitance made it possible to establish that
the amount of the electrolyte in HES of different designs and
capacitance is optimal when about 90-100% of the pores in the
electrodes and separator that are in a fully charged state are
filled with electrolyte. Since the volume of the electrolyte
decreases during the discharge, the rate of the filling of the
pores in the electrodes and separator decreases with an increase of
the depth of the discharge.
[0065] Also note that during the charge of a HES at a high rate,
the electrolyte is partially displaced from the pores in the
electrodes and separator to the capacitor's case. This is related
to the fact that at high rates of charge, the rate of the increase
of the electrolyte's volume is considerably higher than the rate of
diffusion of the electrolyte in the pores of the electrodes and
separator. As a result of this effect, during the charge and
discharge at a high rate and to the maximum state of charge, at the
end stage of the charge process a little amount of free electrolyte
is evolved in the case of the capacitor. In an exemplary method it
is preferable that the volume of free space in that portion of the
case where the electrode pack is placed is small, because a slight
change in the electrolyte's volume brings about a considerable
change of its level. Even filling of the pores of the electrodes
and separator with the electrolyte during its charge and discharge,
results in an effective displacement of the electrolyte and
leveling of its concentration. This effect is especially noticeable
and plays quite a positive role in increasing the cycle life of the
capacitor with a high number of electrodes and large overall
dimension.
[0066] As stated above, the concentration of the electrolyte of a
particular capacitor depends on its design, capacitance, and
purpose. Through experimentation it was discovered that the most
optimal concentration of electrolyte in different capacitors having
a PbO.sub.2|H.sub.2SO.sub.4|C system in the fully charged state is
about 1.24-1.3 g/cm.sup.3 (at the temperature of 25.degree. C.).
After the assembly of the capacitor with pre-formed positive
electrodes, the capacitor is filled with the electrolyte of a
working concentration. In order to fill the capacitor with
non-formed positive electrodes, it is necessary to use an
electrolyte with lower concentration. This is because when the
positive electrodes are formed, the charge Coulombic capacity
(Q.sub.F[Ah]) of the capacitor is determined by the following
formula:
Q.sub.F=kM, (1)
where: k[Ah/kg] is a coefficient having a value of about 440-480
Ah/kg, depending on the manufacturing method and composition of the
active material in the positive electrodes and duration of the
formation process and M[kg] is the mass of the active material of
the non-formed positive electrodes. The maximum specific Coulombic
capacity of the active material (PbO.sub.2) of the formed positive
electrode at 100% depth of its discharge is about 120-125 Ah/kg
(theoretical value of the specific Coulombic capacity PbO.sub.2 has
the value of 224 Ah/kg). Consequently, it is clear from the formula
(1) that during the formation of the positive electrodes a
Coulombic capacity about 3.5 times higher than the actual maximum
Coulombic capacity of the electrodes is used.
[0067] Bearing in mind that usually the Coulombic capacity of the
positive electrodes of a HES is considerably higher than the
Coulombic capacity of the negative electrodes, it is clear that
during the formation of the positive electrodes the Coulombic
capacity needed to form the positive electrodes is several times
higher than the maximum Coulombic capacity of the negative
electrodes. During the formation of the positive electrodes, after
a full charge of the negative electrodes, there occurs evolution of
hydrogen that goes on up to the end of the formation process. This
results in a decrease of the amount of water in the electrolyte and
an increase in the concentration of the electrolyte in the
capacitor. Therefore, according to exemplary method of the present
invention, the capacitor 1 with non-formed positive electrodes is
filled with the electrolyte whose concentration is determined by
the capacitor's design and capacitance. When calculating the
electrolyte's concentration before the formation of the positive
electrodes it is taken into account that after the formation
process the electrolyte's concentration in a fully charged
capacitor should be about 1.24-1.3 g/cm.sup.3.
[0068] In an exemplary method of the present invention a capacitor
1, with non-formed and formed positive electrodes, is filled with
the needed amount and concentration of electrolyte. After the
electrolyte is added to the capacitor with non-formed positive
electrodes, the capacitor was held in normal conditions for about
10-15 minutes for a preliminary impregnation of the electrodes and
separator by the electrolyte. However, for a sufficient filling of
the negative electrodes' pores with the electrolyte under normal
conditions requires about 50-100 hours; depending on the type and
manufacturing method of the carbon material. After the capacitor
has been filled with an electrolyte, a considerable portion of the
electrolyte 17 remains free in the capacitor, even during an
extended exposure under normal conditions. When non-formed positive
electrodes are used, it is preferable that after the capacitor is
filled with an electrolyte, the time of impregnation before the
commencement of formation is not more than about 50-60 minutes.
This is due to the fact that, in the case of extended exposure
sulfation of a considerable portion of the positive electrodes'
active material occurs. As a result, large PbSO.sub.4 crystals may
form and are only partially oxidized to PbO.sub.2 during formation;
this considerably reduces the porosity and Coulombic capacity of
the electrodes and after the formation the active material has a
high content of .alpha.-PbO.sub.2 phase. In addition, the sulfation
of a considerable portion of the active material in the non-formed
electrode substantially reduces the electrolyte's concentration.
This results in an increase of the lead sulfate solubility in the
electrolyte with a low concentration of sulfuric acid. This often
brings about formation of dendrites, increase of self-discharge
current in the capacitors, and more importantly, reduces the cycle
life and service life of the capacitor.
[0069] FIG. 5 illustrates another exemplary method of the present
invention the capacitor 1, with non-formed plates of the positive
electrode, is filled with an electrolyte and then exposed to the
electrolyte for about 15-20 minutes under normal conditions. With
the emergency valve 10 (shown in FIG. 1b) uninstalled, the
capacitor is placed in a vacuum chamber 18 of the installation 19.
The vacuum pump 20 pumps the air out of the vacuum chamber 21 when
the vacuum valve 22 is open. When the pressure in the chamber 21 is
lowered to about 30-40 mm Hg, the vacuum valve 23 is slowly turned
to begin removing air from the chamber 18. The process of pumping
the air from the vacuum chamber 18 and the capacitor 1 continues
until the pressure in the chamber 18 is about 10-15 mm Hg. The
optimal time of exposure of the capacitor 1 in the vacuum chamber
18 at the pressure of about 10-15 mm Hg is about 15-20 minutes
depending on the overall dimensions of the capacitor. After
exposure, the vacuum valve 23 is closed and valve 24 is opened
allowing air to slowly begin to fill the chamber 18.
[0070] After the above procedure only a small amount of free
electrolyte, which will be fully absorbed by the negative
electrodes following the formation of the positive electrodes, is
left in the case of the capacitor 1 and the capacitor is ready for
the formation of the positive electrodes. Research showed that
evacuation (vacuumization) of the capacitor makes it possible to
significantly increase the efficiency of the filling of the pores
and speed up impregnation of the negative electrodes by the
electrolyte.
[0071] In another exemplary method of the present invention
provides for the manufacturing of a HES with the capacitance of
more than 500 kF. During the filling of the electrolyte and
formation of the positive electrodes, a large amount of thermal
energy is generated resulting in excessive overheating and the
electrodes' failure. It is desirable that during the formation of
the positive electrodes the temperature of the capacitor does not
exceed about 50.degree. C. An increase of the temperature over
about 50.degree. C. will result in an irreversible deterioration of
the capacity, power, and cycle life parameters of the positive
electrodes and the active mass of the formed positive electrodes,
after the formation, will consist mostly of .alpha.-PbO.sub.2
phase. In order to manufacture the capacitor 1 with high
capacitance, an exemplary method provides for the use of the cooled
electrolyte to be filed in the capacitor and forced cooling of the
capacitor in the process of the positive electrodes' formation.
[0072] Immediately after the filling of the electrolyte with the
subsequent vacuum pumping of the gases from the electrodes and
separator of a HES 1, with non-formed positive electrodes, a
formation process of the positive electrodes is performed. The
formation of the positive electrodes occurs by passing electric
current through the capacitor causing electrochemical oxidation of
the positive electrodes' active mass forming lead dioxide. The
Coulombic capacity of the formation process is determined by the
formula (1). For the formation of the positive electrodes it is
possible to use different profiles of the charge current. However,
formation by constant current is preferable. This facilitates the
process of formation, and brings about a lower heating of the
capacitor, and the active mass of the positive electrodes are
formed evenly.
[0073] During the formation of positive electrodes by constant
current, the most optimal value of the formation current
(I.sub.F[A]) is determined by the following formula:
I F = Q F t F , ( 2 ) ##EQU00001##
where t.sub.F[h] is the time of formation; Q.sub.F[Ah] is the
Coulombic capacity of the formation which is determined by the
formula (1). The time of formation depends on the design and value
of the capacitors' capacitance, but it is desirable that the time
of formation does not exceed about 60-65 hours depending on the
manufacturing method of the positive electrodes. When the time of
formation is more than 65 hours, usually the active mass of the
electrodes contain macrocrystalline lead sulfate and have low
specific Coulombic capacity. The time of formation is selected to
ensure that during the formation, the maximum temperature of the
capacitor does not exceed about 50.degree. C. Research of the
formation processes of the positive electrodes as components of HES
with different designs and different capacitances showed that the
most optimal formation time of different capacitors with the
capacitance up to 150 kF is about 40-65 hours. When a cooled
electrolyte is used to fill the capacitors and/or using forced
cooling of the capacitors in the process of formation is performed,
the formation time of the capacitors may be lower than the
mentioned values.
[0074] An increase of the temperature of the capacitor's
electrolyte during the formation of the positive electrodes brings
about improvement of the carbon plates' wettability. On the other
hand, an elevated temperature of the electrolyte has a negative
effect on the parameters of the positive electrodes. The results of
different experimental research of the formation process of the
positive electrodes as components of capacitors showed that the
most optimal temperature of a HES during formation of positive
electrodes is about 35-45.degree. C. When the capacitor's
temperature during the formation does not exceed about 45.degree.
C., the active mass of the positive electrodes after the formation
contains mostly .beta.-PbO.sub.2 phase, providing high specific
Coulombic capacity of the positive electrodes and high cycle life
of the capacitors.
[0075] To form the positive electrodes of the capacitor, the
positive electrode's clamps should be connected to the clamps of
the current source, with the pre-set value of the formation
current. During the manufacture of the positive electrodes a thin
oxide layer is formed, reducing the efficiency of formation and
Coulombic capacity of the electrodes. It is desirable to polarize
the positive electrode at the start of formation toward the
negative potentials for about 5-10 minutes. This procedure makes it
possible to reduce the thin oxide layer of the surface of the
positive electrode's grid to the state of lead. Further, the
polarization of the current source changes and continuous formation
of the positive electrodes is performed during t.sub.F time. After
the completion of the formation process, the capacitor's discharge
is performed by the formation current to about 0.8 V voltage of the
capacitor and an emergency valve 10 is fixed in the capacitor. The
capacitor is charged to the optimal voltage, control testing of its
energy and capacity parameters is performed and the capacitor is
ready for operation.
[0076] For the manufacture of a HES 1, with pre-formed positive
electrodes 2, the capacitor is assembled according to the exemplary
method of the assembly of the capacitors with non-formed positive
electrodes. After the assembly, the capacitor is filled with
electrolyte with an appropriate working concentration and in the
needed quantity. It is desirable to ensure that the electrolyte's
concentration is about 1.24-1.3 g/cm.sup.3 (at 25.degree. C.
temperature).
[0077] FIG. 6 illustrates an exemplary method of the present
invention. After the filling the capacitor 1, with formed plates of
the positive electrode, with electrolyte and exposure of the
capacitor without any emergency valve 10 (shown in FIG. 1b)
installed for not less than about 15-30 minutes, under normal
conditions, the capacitor is placed in a vacuum chamber 25 of the
installation 26. The negative current clamp 9 (shown in FIG. 1b) of
the capacitor is connected to the sealed connector 27 and the
positive clamp 9 is connected to the sealed connector 28 and the
vacuum chamber 25 is sealed. The vacuum pump 29 pumps the air from
the vacuum chamber 30 with the vacuum valve in an open position.
After the air is removed from the vacuum chamber 30 to the value of
about 30-40 mm Hg, the vacuum valve 32 is slowly shifted into the
position of the vacuum chamber's 25 pumping. The process of pumping
air from the vacuum chamber 25 and the capacitor 1 continues until
the pressure in the chamber goes down to about 10-15 mm Hg. After
about 25-30 minutes of exposure of the capacitor 1 in the vacuum
chamber 25 at the above values of pressure, the main portion of
free electrolyte is absorbed by the electrodes and separator of the
capacitor. Further, the positive pole of the current source 33 is
connected to the positive clamp of the capacitor 1 and the negative
pole is connected to the negative clamp, and the balancing of the
Coulombic capacities of the positive and negative electrodes of the
capacitors is performed. During the process of balancing of the
Coulombic capacities of the positive and negative electrodes the
process of vacuuming gases from the capacitor continues.
[0078] To provide a serviceable capacitor, it is now necessary to
charge the negative electrodes. It is desirable to ensure that in a
fully charged state, the state of charge of the positive electrodes
does not exceed 90-95%, and the state of charge of the negative
electrodes is about 100%. After filling the capacitor with
electrolytes the capacitor's voltage is about 1.3-1.4 V, depending
on the type of the negative electrodes. During the balancing of the
capacities of the capacitor's electrodes, after a full charge of
the positive electrodes the state of charge of the negative
electrodes will not be high. With an increase in the state of
charge of the negative electrodes, oxygen is evolved in the
positive electrodes, bringing about discharge of the negative
electrodes, impeding the process of balancing.
[0079] In an exemplary method of manufacturing a HES, removal of
the evolved oxygen from the capacitor 1 by vacuumization during its
charge makes it possible to effectively balance the Coulombic
capacities of the capacitor's positive and negative electrodes.
Research makes it possible to establish that the Coulombic capacity
(Q.sub.B[Ah]) of the process of balancing the electrodes of HES of
different designs and different Coulombic capacities is very well
characterized by the following formula:
Q.sub.B=1,5Q.sub.N, (3)
where Q.sub.N[Ah] is the Coulombic capacity of the negative
electrodes at the maximum state of charge of the capacitors. For
the balancing of the electrodes' capacities it is possible to use
different profiles of the charge current, but the balancing by
constant current is preferable as it facilitates the formation
process and brings about lower overheating of the capacitor. This
is particularly important to the balancing of the capacitors of
high capacitance. The value of the balancing charge current
I.sub.B[A] is expressed by the formula:
I B = Q B t B , ( 4 ) ##EQU00002##
where t.sub.B[h] is duration of balancing process.
[0080] The balancing of the Coulombic capacities is performed by
I.sub.B current whose value is pre-set in the current source 33 up
to its completion. At the final stage of the balancing process,
apart from the oxygen evolution in the positive electrode, hydrogen
is often evolved in the negative electrode. Both the oxygen and
hydrogen are removed from the volume of the capacitor by the
process of pumping off gases from the capacitor. This makes it
possible to prevent the process of displacement of electrolyte, by
hydrogen, from the negative electrodes' pores and provide for an
effective balancing of the Coulombic capacities of the capacitor's
positive and negative electrodes.
[0081] After the completion of balancing the Coulombic capacities
of the capacitor with pre-formed positive electrodes, the capacitor
is discharged by the balancing current until the capacitor's
voltage reaches about 0.7-0.8 V, while continuing to pump gas from
the capacitor. Further, the vacuum valve 32 is closed using the air
inflow valve 34 and the vacuum chamber (25) is filled with air. As
soon as the atmospheric pressure is reached in the chamber 25, the
chamber opens and the emergency valve (10) is installed in the
capacitor. The capacitor is charged to the optimal voltage, its
clamps are disconnected from the connections, and the capacitor is
extracted from the vacuum chamber for control testing of its
energy, capacity parameters and operation.
EXAMPLES
Example 1
[0082] Example 1 is an HES manufactured using an exemplary method
of the present invention showing the efficiency of the an exemplary
method. FIG. 1a is a capacitor (HES #1) having a
PbO.sub.2|H.sub.2SO.sub.4|C system was manufactured with
10.sub.+/11.sub.- plate count of positive and negative electrodes.
In order to manufacture the HES #1, non-formed plates of the
positive electrodes 2 with a dimension of 193.times.159.times.2.6
mm.sup.3 were used. The total mass and active material mass of 10
non-formed plates of the positive electrodes of the capacitor 1 was
4.0 kg and 2.65 kg respectively. The maximum Coulombic capacity of
the plate of the formed positive electrode during 12-hour discharge
is 30 Ah.
[0083] To manufacture the negative electrodes 11, a carbon plate
(3) having an overall dimension of 193.times.159.times.2.0 mm.sup.3
was used. The total mass of 20 carbon plates of HES #1 was 675 g.
The mass density of the dry carbon plates was 0.55 g/cm.sup.3. The
maximum specific capacitance and Coulombic capacity of the carbon
plates during the measurements thereof as components of the
capacitor having a PbO.sub.2|H.sub.2SO.sub.4|C system were 660 F/g
and 860 C/g respectively.
[0084] Lead alloy current collectors containing 3% Sn having a
conductive protective coating 12 were used as the current
collectors 4 for the negative electrodes. The protective coating
was made of chemically stable polymers and carbon powders with high
conductivity. The current collectors had an overall dimension of
193.times.159.times.0.26 mm.sup.3.
[0085] The negative electrodes 11 and 14 are made by pasting 15 the
carbon plates 3 to the current collectors 4. A conductive adhesive
layer 13 of about 5 .mu.m thickness was applied on the surfaces of
the protective coating 12 of the current collectors. The carbon
plates were pasted by the rolling of the joint current collectors
with the carbon plates. The pressure of the cylinder rolls 16 on
the carbon plates during rolling was about 0.6 kg/cm.sup.2.
[0086] An AGM separator of 0.5 mm thickness (at 20 kPa pressure)
was used as the separator 5 in this exemplary method. The electrode
pack and capacitor were assembled together in the exemplary method
stated above. In order to cast the terminals with the jumpers of
the positive and negative electrodes, a lead alloy with 5% content
of antimony was used.
[0087] HES #1 was filled with 1.3 kg of the electrolyte 17 of
aqueous solution of sulfuric acid having 1.24 g/cm.sup.3 density
(at 25.degree. C. temperature). The electrolyte's temperature
before the filling in the capacitor was 20.degree. C. The
calculated density of the electrolyte after the formation of the
positive electrode's plates was 1.26 g/cm.sup.3. The capacitor was
exposed to the electrolyte for 15 minutes under normal conditions.
For the maximum filling of the carbon plates' pores, the capacitor
was subjected to vacuumization by the afore-mentioned exemplary
method for 20 minutes at a vacuum chamber pressure of 10 mm Hg.
After the vacuumization, the capacitor's temperature increased to
42.5.degree. C.
[0088] The positive electrodes of the HES #1 were formed in the
continuously by a 20 A constant current for 60 hours. The Coulombic
capacity of the formation had the value of 1200 Ah. The ambient
temperature during the formation changed in the range of
20-21.degree. C.
[0089] FIG. 7 illustrates the voltage of the HES #1 before the
formation process (when there was no formation current) at about
minus 0.57 V and when the formation current is switched on
increasing in rapidly to the value of about 1.65 V. Further, the
voltage of the capacitor increases in a monotonic manner and during
4 hours reaches a value of about 2.6 V. Thereafter, a slight
decrease of the voltage occurs and then the voltage increases in a
monotonic and slow manner. During the final stage of the formation,
the capacitor's voltage does not change and at the end of the
formation is 2.65 V.
[0090] FIG. 8 is a diagram plotting temperature versus time. The
temperature of the HES #1 has the maximum value of 42.5.degree. C.
before its formation. At the initial stage of formation the
capacitor's temperature decreases to 41.5.degree. C. in a rapid
manner. Thereafter, as the formation process continues, the
capacitor's temperature does not change and remains about
39.degree. C. This example shows that during the formation of the
capacitor's positive electrodes its maximum temperature does not
exceed 42.5.degree. C., and the average value of the temperature is
39.2.degree. C., making it possible to perform effective formation
of the positive electrodes and perform balancing of the Coulombic
capacities of the positive and negative electrodes.
[0091] After the completion of the formation process of HES #1's
positive electrodes, the capacitor was discharged by 15 A constant
current to the voltage of about 0.7 V. The maximum values of the
discharge energy and Coulombic capacity of the capacitor were 212
Wh and 158 Ah respectively (See Table 1). The maximum capacitance
of the capacitor after the formation of the positive electrodes has
a value of about 435 kF. Since the maximum value of the specific
capacitance of the carbon plates is about 660 F/g and the total
mass of the carbon plates in the capacitor is equal to about 675 g,
it is clear from the values of the capacitor's capacitance that
after the formation the main pores of the carbon plates were fully
filled with the electrolyte.
[0092] After assembly of the HES #1 its mass, without electrolyte,
was 6.2 kg, and after the addition of the electrolyte and the
positive electrodes' formation the mass was about 7.5 kg, the
maximum specific energy of the capacitor has the value of about
28.2 Wh/kg by mass.
[0093] The density of the capacitor's electrolyte after its
formation showed an increased to 1.261 g/cm.sup.3 (at T=25.degree.
C.) that is well in line with the estimate value of the density
(1.26 g/cm.sup.3).
[0094] After the discharging the HES #1 down to a voltage of 0.7 V
in order to seal the capacitor, an emergency valve was fixed in the
capacitor. Thereafter, testing was performed of the energy and
capacity parameters of the sealed HES #1 at an ambient temperature
of 25.degree. C. and in different modes of charge and discharge.
The values of charge (I.sub.Ch) and discharge (I.sub.dis) currents,
charge (Q.sub.Ch) and discharge (Q.sub.dis) Coulombic capacity,
discharge energy (E.sub.dis), and voltage of the HES #1 at the end
of the charge (U.sub.ech) are shown in Table 2. In all the testing
modes, the capacitor is discharged to the voltage of 0.8 V.
[0095] As the state of charge of the HES #1 increases from 95 Ah to
150 Ah, the voltage U.sub.edis increases from about 2.281 V to
2.362 V (Table 2). The slow increase in the voltage of the HES at
its high state of charge (as it was shown above) is related to an
increase of the negative electrode's capacitance, a heavy shift of
its potential toward the negative area of the potentials. It
follows from FIG. 9, that at low values of the state of charge the
capacitors' voltages increase linearly. Furthermore, along with an
increase of the state of charge, the voltage's increase slows.
Example 2
[0096] Example 2 is another exemplary method of the present
invention where a capacitor, HES #2, was manufactured having the
same dimensions of the positive and negative electrodes and design
of the capacitor shown in Example 1. The filling of the capacitor
with electrolyte is performed by the method shown in Example 1. The
positive electrodes of the HES #2 were formed by 22.5 A constant
current for 53 hours.
[0097] The voltage of HES #2 changes during the formation similarly
to the voltage change of HES #1. FIG. 8 indicates that the
temperature of HES #2 at the start of formation is about
43.5.degree. C. Unlike the temperature change of HES #1, the
temperature change of HES #2 at the initial stage of formation
decreases slower. At the final stage of formation, there occurs a
slight increase in temperature, and the average value of the
capacitor's temperature during the formation is 40.1.degree. C. HES
#2 has a higher average value of the temperature as compared to the
average temperature of HES #1, because of the higher formation
current 22.5 A.
[0098] The maximum capacitance of HES #2 is 447 kF as shown in
Table 1. HES #2 has a higher value of capacitance as compared to
the capacitance 435 kF of HES #1. The high temperature improves the
wettability of the carbon plates by the electrolyte resulting in
elevated values of the capacitor's capacitance.
[0099] The maximum discharge energy and Coulombic capacity of HES
#2 are 218 Wh and 162 Ah respectively, and has a maximum specific
energy of 29.1 Wh/kg. Testing of the energy and capacity parameters
in different modes of charge and discharge shows that the discharge
energy and Coulombic capacity of HES #2 have higher values than
those of HES #1, as recorded in Table 2. The higher capacity
parameters of HES #2 also become clear from looking at the time
dependence of the voltage during its charge and discharge by 15 A
constant current as seen in FIG. 9.
Example 3
[0100] Example 3 is another exemplary method wherein a capacitor,
HES #3, was manufactured with the same dimensions of positive and
negative electrodes of the capacitor design shown in Example 1.
Before, HES #3, was filled with electrolyte, the electrolyte was
cooled to a temperature of about minus 25.degree. C. The
electrolyte had a density of about 1.24 g/cm.sup.3. Further, the
capacitor was slowly filled with electrolyte and left to expose for
15 minutes. Then the capacitor was vacuumized. The pressure in the
vacuum chamber was about 10 mm Hg and the duration of the
vacuumization process was about 20 minutes. The capacitor's
temperature after the vacuumization increased to 26.degree. C.
[0101] At the start of the formation process, the positive
electrodes were polarized toward the negative area of the
potentials by a 20 A current and the negative electrodes polarized
toward the positive area to recover the oxide layers on the
surfaces of the positive electrodes' grids. After 10 minutes, the
current's direction was changed, and the positive electrodes were
continuously formed by the assigned 20 A current over 60 hours.
[0102] FIG. 7 shows the voltage of HES #3 during the formation was
lower than the voltage of HES #1 and HES #4. At the end of the
formation process there was a slight decrease of the voltage
relating to the increase in temperature. FIG. 8 shows the
temperature of HES #3 at the initial stage of formation increases
slowly to 35.degree. C. Further, with an increase of the formation
time, the temperature's change is insignificant and at the final
stage of formation the temperature increases to 37.2.degree. C. The
capacitor's average temperature during the formation was
34.7.degree. C.
[0103] The capacitance of HES #3 is 430 kF, and the maximum value
of the discharge energy and Coulombic capacity are 210 Wh and 156
Ah respectively, as shown in Table 1. Testing of the energy and
capacity parameters of HES #3 show the capacitor has high energy
and capacity parameters as seen in Table 2. The use of a cold
electrolyte maintains a colder average temperature of the capacitor
during formation, and the positive electrodes are formed
effectively. The use of a cold electrolyte will make it possible to
considerably decrease the time of formation of positive electrodes
of a high capacitance HES.
Example 4
[0104] Example 4 is another exemplary method wherein a capacitor,
HES #4, was manufactured with the same dimensions of the positive
and negative electrodes and design of the capacitor specified in
Example 1. The electrolyte has a density of about 1.24 g/cm.sup.3
and was added to the capacitor in the same manner as Example 1. The
positive electrodes of HES #4 were formed by a 25 A constant
current over 48 hours. In the course of the formation process, the
capacitor's temperature was forcibly and uniformly maintained at
about 25.degree. C.
[0105] FIG. 7 shows that the voltage of HES #4 during the formation
increases slowly and after 18 hours reaches about 2.76 V; then a
slight voltage drop takes place. At the end of the formation, the
capacitor's voltage is about 2.66 V.
[0106] The capacitance of HES #4 is 426 kF, and the maximum
discharge energy and Coulombic capacity are 208 Wh and 154 Ah
respectively, as shown in Table 1. The reduced values of
capacitance and discharge energy of HES #4 as compared to the same
parameters of HES #1, #2 and #3, shown in Table 2, is mostly
related to the reduced temperature during the capacitor's
formation.
Example 5
[0107] Example 5 is another exemplary method wherein a capacitor,
HES #5, was manufactured with a 10.sub.+/11.sub.- positive and
negative electrode plate count and having the same design shown in
FIG. 1a. To manufacture HES #5, non-formed plates of the positive
electrodes with 207.times.172.times.2.38 mm.sup.3 overall
dimensions were used. The total mass of 10 non-formed plates of
positive electrodes and their active materials had values of 4.6 kg
and 2.84 kg respectively. The maximum Coulombic capacity of the
formed positive electrode during a 20 hour discharge was 32.6
Ah.
[0108] The carbon plates of the negative electrodes had dimensions
of about 207.times.172.times.2.2 mm.sup.3. The total mass of 20
carbon plates in the HES #5 was 970 g. The maximum specific
capacitance and Coulombic capacity of the carbon plates having a
0.65 g/cm.sup.3 density was about 795 F/g and 1040 C/g
respectively.
[0109] The current collectors of the negative electrodes had a
similar design of the current collector found in HES #1 and overall
dimensions of 207.times.172.times.0.26 mm.sup.3. The negative
electrodes were made according to the manufacturing methods found
in HES #1. An AGM separator of 0.5 mm thickness was used. The
assembly of HES #5 was performed similar to the assembly of HES #1.
The mass of HES #5 without the electrolyte was about 7.4 kg.
[0110] After assembly, HES #5 was filled with approximately 1.95 kg
of aqueous sulfuric acid electrolyte having a density of about 1.23
g/cm.sup.3 at 25.degree. C. The electrolyte's temperature before
addition to the capacitor was 20.degree. C. After 15 minutes of
exposure under normal conditions, the capacitor was vacuumized for
20 minutes at a pressure of 10 mm Hg. After the electrolyte
addition and vacuumization, the capacitor's temperature was about
38.2.degree. C.
[0111] The formation of the positive electrodes of HES #5 was
performed by a 20 A constant current. The formation Coulombic
capacity was 1280 Ah and duration of 64 hours.
[0112] FIG. 10 shows that at the initial stage of formation the
capacitor's temperature increases fast and after 2.5 hours reaches
a maximum of 46.6.degree. C. Thereafter, during the course of
formation, the temperature of HES #5 decreased to about
35.5.degree. C. and then slowly increased until the end of the
formation process. At the end stage of the formation phase the rate
of temperature rise increases, and at the end of formation the
capacitor's temperature reaches 40.4.degree. C. During the
capacitor's formation its average temperature was 38.5.degree. C.
at an average ambient temperature of 21.9.degree. C.
[0113] The voltage of HES #5 immediately after the addition of
electrolyte and vacuumization had a value of about minus 0.558 V,
and after the formation current was turned off it increased
unevenly to about 1.58 V, as shown in FIG. 10. Then the capacitor's
voltage increases in a monotonic manner and after 10 hours reaches
a value of about 2.4 V. After 10 hours, the increase of the
capacitor's voltage gradually slows as the formation continues. At
the end of the formation process the capacitor's voltage is about
2.488 V.
[0114] The density of the HES #5 electrolyte immediately after the
formation of the positive electrodes was about 1.3 g/cm.sup.3 (at
T=25.degree. C.). Immediately after the completion of the formation
process, the capacitor was discharged by a 20 A constant current to
the voltage of 0.7 V. Then the capacitor was sealed. The maximum
values of the discharge energy and Coulombic capacity of HES #5
were 382 Wh and 280 Ah respectively; the maximum capacitance was
about 770 kF, as shown in Table 1. The maximum specific energy, by
mass, of the capacitor was about 41.0 Wh/kg.
[0115] The energy and capacity parameters of HES #5 were tested in
three different modes of charge and discharge at 25.degree. C.
ambient temperature. The capacitor was charged and discharged by a
25 A constant current with 125 Ah, 175 Ah and 250 Ah charge
Coulombic capacity. In all the modes, the capacitor was discharged
to the voltage of 0.8 V. The energy and capacity parameters of HES
#5 are shown in Table 2. At the values of 125 Ah, 175 Ah and 250 Ah
of the charge Coulombic capacity the specific discharge energy of
the capacitor was 18.4 Wh/kg, 25.8 Wh/kg and 34.3 Wh/kg
respectively.
[0116] It follows from FIG. 11 that at the charge Coulombic
capacity of 125 Ah, 175 Ah and 250 Ah the parameters of the time
dependence of the voltage of HES #5 are not different from the
parameters of the time dependence of HES #1 and #2, as shown in
FIG. 9. We should note that during testing with the charge
Coulombic capacity of 250 Ah, a slight decrease of the voltage of
HES #5 during the final stage of the charge process occurred, as
shown in FIG. 11. This is related to the fact that at a high state
of the capacitor's charge an increase of its temperature takes
place. Since an increase of the capacitor's temperature results in
a decrease of the internal resistance, the overpotentials of
evolution of hydrogen of the negative electrode and oxygen of the
positive electrode, and a slight decrease of the voltage takes
place along with an increase of the capacitor's temperature.
Example 6
[0117] Example 6 is another exemplary method of the present
invention. To show the efficiency of the proposed exemplary
manufacturing method of HES with pre-formed positive electrodes, a
capacitor was manufactured, HES #6, with 10.sub.+/11.sub.- positive
and negative electrode plate count and having the design shown in
FIG. 1a. The formed positive electrodes 2 have a dimension of about
185.times.170.times.2.1 mm.sup.3. The total mass of 10 plates of
the positive electrodes of the capacitor 1 was about 3.8 kg. The
maximum Coulombic capacity of the positive electrode during a 20
hour discharge was about 25 Ah.
[0118] The negative electrodes were made of carbon plates 3 with an
overall dimension of 185.times.170.times.2.0 mm.sup.3 and current
collectors 4 with an overall dimension of about
185.times.170.times.0.26 mm.sup.3. The current collectors had a
protective coating 12 and negative electrodes 11 and 14 were
manufactured as per the method described in Example 1.
[0119] The mass density of the dry carbon plates of HES #6 were
about 0.53 g/cm.sup.3 and the total mass of 20 carbon plates was
about 650 g. The maximum specific energy and Coulombic capacity of
the carbon plates were about 615 F/g and 803 C/g respectively.
[0120] An AGM separator of 0.5 mm thickness (at 20 kPa pressure)
was used as the separator 5. The assembly of HES #6 was performed
by the exemplary method used to construct HES #1, shown in Example
1. The mass of HES #6 without the electrolyte was about 5.95
kg.
[0121] HES #6 was filled with 1.15 kg electrolyte 17 of sulfuric
acid aqueous solution having a density of about 1.26 g/cm.sup.3 at
25.degree. C. temperature. After 30 minutes of exposure under
normal conditions, the capacitor was placed in the vacuum chamber
25 of the installation 26, shown in FIG. 7. The capacitor was
vacuumized for 30 minutes. The pressure in the vacuum chamber was
about 10 mm Hg. Following the vacuumization, the capacitor's
temperature increased to about 26.5.degree. C.
[0122] The current clamps 9 of the capacitor were connected to the
sealed connectors 27 and 28 as shown in FIG. 7. The poles of the
current source 33 were connected to the connectors 27 and 28 as
shown in FIG. 7. The balancing of the Coulombic capacities of the
positive and negative electrodes of HES #6 was performed by a 14 A
constant current for 15.5 hours while the vacuum chamber was
continuously pumped off. After the balancing current was switched
on, the gases'pressure in the vacuum chamber increased to 15 mm Hg
after 25 minutes. After 50 minutes, the pressure was decreasing to
10 mm Hg and remained unchanged until the end of the balancing
process.
[0123] As shown in FIG. 12, the voltage of HES #6 was about 1.376 V
before the balancing current was switched on, and the temperature
was about 26.5.degree. C. While an increase in the time required
for balancing the capacitor's voltage (U.sub.C) increases in a
monotonic manner, the temperature (T.sub.C) decreases
insignificantly. Further, after 11 hours of balancing the
capacitor, the value U.sub.C reaches its maximum value of about
2.62 V; then decreases in a monotonic manner until the end of the
balancing process. At the end of the balancing process the U.sub.C
is about 2.53 V. A decrease of the capacitor's voltage at the final
stage of the balancing process is related to an increase of its
temperature. When the negative electrodes of the capacitor are
fully charged, there occurs an abrupt increase in the evolution of
hydrogen and heat that results in a fast increase in the
capacitor's temperature, as shown in FIG. 12. At the end of the
balancing process the temperature of HES #6 was about 31.9.degree.
C.
[0124] The maximum voltage of a HES during the balancing of the
capacities of the positive and negative electrodes is mostly
related to the rate of the removal of gases from the capacitor, the
balancing current used, overall dimensions of the electrodes, and
the value of the capacitance of the capacitor. According to
exemplary manufacturing methods of the present invention, the
Coulombic capacities of the positive and negative electrodes of a
HES with pre-formed positive electrodes are effectively balanced
when the Coulombic balancing capacity, after maximum voltage of the
capacitor is obtained, is not less than 10% of the Coulombic
balancing capacity before obtaining the maximum value of the
capacitors' voltages. In the case of balancing the capacities of
the electrodes of a capacitor having two or more plates of the
positive electrodes, apart from the balancing of the electrodes'
capacities, the balancing process brings about a maximum leveling
of the state of charge of all the plates of the positive
electrodes. This increases the stability of the energy, capacity
parameters, cycle life, and reliability of the capacitor's
operation.
[0125] Since the positive electrodes of the capacitor are
pre-formed there is no risk of active material sulfation during
extended exposure in the electrolyte and the duration of the
balancing process may be increased. However, extending the
balancing process increases cost and manufacturing time of the
capacitors. Therefore, the optimal duration of the balancing
process is selected to ensure that during the balancing the
capacitor's temperature does not exceed about 50.degree. C. Usually
the optimal duration of the balancing process of HES electrodes
with a capacitance of up to 400 kF does not exceed 16 hours and
capacitances between 400 kF and 800 kF do not exceed 20 hours.
[0126] The discharge of HES #6 by a 14 A current to a voltage of
about 0.7 V, immediately after the balancing process, indicated
that the maximum capacity and maximum discharge energy have values
of 145 Ah and 194 Wh respectively. The maximum capacitance of the
capacitor is 398 kF, as shown in Table 1; this indicates that the
capacitor's negative electrodes during balancing are fully charged.
The mass of HES #6 before electrolyte addition was about 6.0 kg and
after the electrolyte addition and balancing about 7.1 kg. The
maximum specific (by mass) energy of the capacitor has a value of
about 27.3 Wh/kg.
[0127] After the discharge of HES #6 to a voltage of 0.7 V and
affixing an emergency valve, the energy and capacity parameters
were tested at an ambient temperature of about 25.degree. C. The
capacitor was charged and discharged by a 13 A constant current in
three different modes. The value of the charge Coulombic capacity
of the first, second and third modes was 75 Ah, 100 Ah and 110 Ah
respectively. In all the modes the capacitor was discharged to the
voltage of 0.8 V. The energy and capacity parameters of HES #6 are
shown in Table 2.
[0128] At the charge Coulombic capacity of 75 Ah, 100 Ah and 110
Ah, the pattern of the time dependence of the voltage of HES #6 are
different from the patterns of the time dependences of HES #1 and
#2 (FIGS. 13 and 9). FIG. 13 indicates that during testing with the
charge Coulombic capacity of 110 Ah, at the end of the charge
process there is a slight decrease of the voltage of HES #6 which
is a result of the increase in the capacitor's temperature at the
final stage of the charge process.
[0129] The exemplary embodiments described are given by example and
should not be used to limit the present invention. It is understood
by one skilled in the art may manufacture a HES with different
dimensions and configurations of the positive and negative
electrodes and capacitors. The capacitors may be manufactured with
the capacitance from several millifarads to several megafarads.
During the formation of the positive electrodes or balancing of the
Coulombic capacities of the positive and negative electrodes,
constant current may be used whose value changes in a different way
during these processes.
TABLE-US-00001 TABLE 1 Maximum energy, capacity parameters of a HES
and parameters of the positive electrodes formation modes. Maximum
parameters of Capacitors capacitors HES-#1 HES-#2 HES-#3 HES-#4
HES-#5 HES-#6 Capacitance, 435 447 430 426 770 398 kF Coulombic 158
162 156 154 280 145 capacity (during discharge to 0.7 V), Ah
Discharge 212 218 210 208 382 194 energy (during discharge to 0.7
V), Wh Discharge 203 208 201 199 368 186 energy (during discharge
to 0.8 V), Wh Specific 28.2 29.1 28.0 27.7 41.0 27.3 (by mass)
energy, Wh/kg Specific 54.8 56.3 54.3 53.7 89.2 52.4 (by volume)
energy, Wh/l Formation 20 22.5 20 25 20 14 current (balancing), A
Formation time 60 53 60 48 64 15.5 (balancing), hour Volume, I 3.87
3.87 3.87 3.87 4.28 3.71 Mass, kg 7.5 7.5 7.5 7.5 9.3 7.1
TABLE-US-00002 TABLE 2 Energy and capacity parameters of a HES in
the different modes of charge and discharge at 25.degree. C.
temperature. Parameters I.sub.ch, I.sub.dis, Q.sub.ch, Q.sub.dis,
E.sub.dis, U.sub.ech, Capacitors A A Ah Ah Wh V HES-#1 15 15 95
90.7 131.6 2.281 15 15 140 130.2 184.4 2.358 15 15 150 137.4 193.4
2.362 HES-#2 15 15 95 93.2 135.8 2.278 15 15 140 132.8 189.5 2.352
15 15 150 140.3 194.7 2.358 HES-#3 15 15 95 89.8 130.2 2.285 15 15
140 129.1 182.3 2.362 15 15 150 135.8 191.1 2.367 HES-#4 15 15 95
89.3 128.9 2.287 15 15 140 127.8 180.6 2.364 15 15 150 134.5 189.4
2.369 HES-#5 25 25 125 120.6 171.1 2.187 25 25 175 168.5 240.1
2.291 25 25 250 228.5 318.6 2.396 HES-#6 13 13 75 73.3 104.2 2.253
13 13 100 92.5 130.4 2.315 13 13 110 98.4 137.3 2.313
* * * * *